Audiphone



sept. 23, 1952 J, M, HAZARD 2,611,829

AUDIPHO NE Filed June 17, 1949 RELATIVE VELOC\TV' |00 500 OOO .|500 2000 SOOO 4000 FREQUENCY m CYCLES Pen sacem?, Z9 3 /Z 5 /9 7 16 T F G 2 I i INVEN OR Patented Sept. ?.'5,J1952` AUDIPHONE Jarvis M. Hazard, Bellerose, N. Y., assigner to Dictograph Products Company, Inc., New York, N-` Y., a corporation of Delaware Application June 17, 1949, Serial No. 99,657

6 Claims. (Cl. 179-107) This invention relates to audiphones, and has particular reference to audiphone receivers having a vibrating element adapted to be operatively connected to the skin overlying thebone structure of the user for transmitting audible sounds picked up by a suitable microphone to the inner ear through the skin of the user.

Audiphone receivers are either of the air conduction or the bone conduction type and the latter type generally consists of an electromagnetically-vibrated member mounted within a casing in such 'a way that the casing with its integral contactor pressed against the skin is bodily vibrated by the reaction of the vibratory member. or a separate skin contactor is connected to a vibratory member through an opening in the casing. The former type is generally known as the reaction or indirect action receiver while the latter type is generally known as the direct action receiver. Both types are mounted on the head by means of a headband functioning not only to support thev receiver, but also to supply sumcient pressure` to the lcontactor thereof to compress the skin overlying the bone so that it constitutes an essentially non-resilient transmitting medium between the vibrating contactor and the underlying bone. 'I'he average pressure with which the contactor is applied to the skin by the headband is usually on the order of eight ounces, but it may be more, especially when the skin of the wearer is particularly soft as when a layer of fatty tissue lies between the skin and the bone. Y

In order to preclude impairment of the operation of the direct-acting type of receiver by this relatively high pressure applied by the headband, the spring between the contactor and the magnetic unit has been made sufllciently stiff to prevent suppression of the vibration by freezing of the magnetic air gap, as 'is proposed in Koch Patent No. Re. 22,658. The alternative expedient of allowing the contactor to recede under headband pressure and adjusting the magnetic air gap accordingly has been proposed in Lieber Patents Nos. 1,940,553 and 2,077,425. It has also been suggested in Goldschmidt Patent No. 2,402,392 that the receiver be held against the head by cooperation of a magnet in the receiver with an armature inserted by surgery between the bone and the skin, thus making a headband unnecessary. All of these arrangements presuppose the necessity of a, pressure on the order of about eight ounces to compress the skin so that it transmits the vibrations.

Applicant has discovered that vibrations within the audible frequency range may be transmitted by a vibratory contactor applied without pressure to the skin, such as that overlying the mastoid eminence, and excellent conduction thereof to the inner ear obtained in cases where tests show that bone reception is indicatedl provided that the resonance frequency of the contactor is continuously adjusted so as to emphasize the message-carrying consonants of the transmitted speech sounds. c

In accordance with this discovery, an audiphone receiver is provided in which the mass and stiffness constants are so chosen that the voice currents picked up by a suitable microphone are made to vibrate a, contactor in pressureless engagement with the skin at audible frequencies having a resonance peak which automatically shifts as the intensity of the transmitted sound changes, so that the speech-carryingweak consonant sounds are emphasized and the vibrations are transmitted with a high degree of intelligiblity and fidelity to the inner ear of the user.

More particularly, the response characteristics of the audiphone receiver of this invention are such that resonance peak automatically shifts from a region below 1,000 cycles persecond for the normally loud vowel sounds to aregion above 1,000 cycles per second for the normally weak consonant sounds. In other words, the resonance frequency in cycles per second varies inversely as the intensity of the sounds transmitted to the receiver, and as virtually each spoken word contains both vowels and consonants the peak shifts at least once from lowV to highv or vice versa during the transmission of each word.

This remarkable eiect is obtained with a iight weight and simply constructed receiver whose contactor may be cemented to the skin without the need of a headband and without requiring any pressure, but, on the contrary, negative contactor pressure results, since the weight of the unit tends to pull the contactor away from the skin, thereby placing the latter in tension instead of compression as when a headband is used.

Although the audiphone receiver of this invention may take different forms, a preferred embodiment thereof comprises a circular contactor driven by a disc diaphragm or armature spaced by a, narrow air gap from the pole shoes of an electromagnetic unit having a voice coil adapted to be energized by' amplified microphone currents. The electromagnetic unit is housed in a casingwhich has a peripheral flange overlapping the edge ofthe contactor without limiting the freedom of vibration of the latter. The contactor is adapted to rest against the skin as by being cemented thereto, and accordingly car ries the electromagnetic unit, which is not otherwise supported. The diaphragm has a spring stiiness such that it frees itself from the pole shoes when the pressure urging it against the latter is released. Although the magnetic traction is the only force which holds the diaphragm in spaced relationto the pole shoe, the flux varies in accordance with the momentary changes in the voice currents so that the compliance of the diaphragm varies correspondingly. even though the free unrestrained mass of the electromagnetic means remains fixed4 Hence, the natural frequency of the vibrating system changes, and the masses are so arranged that l 3 resonance occurs at the aforementioned regions. Also, the vibration ofthe casing is so reduced that acoustic feed-begr is substantiallyl precluded.

It will be seen that the new audiphone receiver of this invention is simple, effective and comfortable to wear, and is free of the objections of ear-supported and headband-supported receivers, while at the same time lends itself to standardization for quantity production.

For a more complete understanding of the invention. reference may be had to the accom panying drawings, in which:

Figure 1 illustrates the audiphone receiver of this invention mounted on the head of a user over the mastoid eminence;

Fig. 2. is an axial section through a greatly enlarged view of the instrument as seen along the line v2--2 of Fig. 3;

Fig. 3 is a face view Fig. 2;

Fig. 4 illustrates a partial section through an adhesive wafer cartridge; and

Fig. 5 illustrates a family of resonance curves of the new receiver and shows the manner in which the peak shifts for input sounds of different intensity levels.

Referring to Figs. 2 and 3 of the drawings, numeral I0 designates the audiphone receiver of this invention which may be mounted on the head of the user by adhesive in the manner illustrated in Fig. l.

The receiver I 0 consists of a relatively rigid electromagnetic unit Il, a vibratory member I2 and a housing I3 comprising the casing I4 and clamp ring I5. The electromagnetic unit II comprises the frame I6 having a recess in its lower surface in which is mounted the circular plate I1 peened in place as shown. Mounted on plate I1 is a ring-shaped permanent magnet I 8 of suitable magnetic material such as an aluminum-nickel-cobalt alloy.

Also mounted on plate I1 is the pole shoe I9 carrying the voice coil 2D whose terminals are adapted to be separably connected by a plug 2l to the receiver cord 22. When the plug 2| is inserted in the corresponding socket of the casing I4, the voice coil is series-connected in the speech input circuit containing a microphone 23. switch 24. battery 25, and the usual amplifier, volume control and the like, not shown.

'Ihe magnet frame I6 is provided with a peripheral bead 28 forming a knife-edge seat for the diaphragm 21 which normally spaces the under surface of the diaphragm 21 from the magnet I8 and Dole shoe I9 a distance of between .001 and .002 inch, which constitutes the air gap. 'I'he diaphragm 21 is preferably formed of soft steel and has a thickness on the order of .005 inch and a diameter on the order of .724 inch. A at steel disc or slug 28 is welded to the outer surface of the diaphragm 21 and to the slug 28 is cemented a button 2S of suitable plastic material. this button having a peripheral flange which is overlapped but not touched by the edge of the clamping ring I5. as shown. The button 29 is preferably shaped to conform to the contour of a selected portion of the wearer's body. such as slightly concave to fit the mastoid eminence to which it may be adhered by adhesive wafer 30. to be described.

The preferred overall diameter of the receiver III is on the order of .8 inch. the diameter of the button 29 on the order of .65 inch, the overall height on the order of .45 inch, and a'space beof the receiver shown in tween the lower surface of the button 29 and the diaphragm 21 is on the order of .011 inch. IJ'll'he preferred weight of the vibratory member I2, consisting of the diaphragm 21, slug 28 and button 29 is .O4 ounce. The preferred weight of the magnetic unit II, plus the weight of the casing I4 and clamp ring I5, is .25 ounce, makinga1tota.l2weight of .29 ounce. Inasmuch as the receiver -I0 is'normally worn with its dia- Dhragm Zlubstantially vertical, and as the vibratory member I2 is a separate element from the relatively heavy magnetic unit assembly II, I3, the latter is urged by gravity outwardly and downwardly away from the vibratory memberA I2. Aocordingly,not only is the supporting skinunder negative pressure or tension, but it is only the staticv magnetictracticn of the electromagnetlc unit/,II that holdsthe diaphragm 21 at the optimum airgap spacing. since the edge of the clamp ring I5 iwhich overlaps the flange of the button 29 does not engage or hold the button 29. Inasmuch as the diaphragm has a spring stiffness such that it frees itself from the pole shoes when freezing pressure is released, and since the static flux has imposed thereon the momentary flux variations caused by the voice currents. the compliance of the diaphragm changes in accordance with the flux changes.

In these circumstances, the vibratory mem ber I2 may be regarded as a body vibra-ting between the surface of the skin and the magnetic unit assembly II, I3, neither -ofwhich exerts pressure on the vibratory member I2, nor any appreciable restraint except that imposed by the varying flux across the air gap during operation.

The receiver of this invention accordingly is fundamentally-different from the reaction type bone receiver in `that the latter employsa stiff spring between the magnetic unit and the armature, which imposes a substantial restraint on the freedom of vibration of the armature.

The new receiver is also fundamentally different from the direct action bone receiver. not only in that a stiff armature spring opposing headband pressure or a headband-positioned soft spring is there employed, but also because the pressure with which the button or other contact surface must be applied to the skin by a headband imposes a substantial restraint on the freedom of vibration of the armature.

This freedom of vibration of the vibratory member I2 of the receiver of the present invention enables a standard unit to be made which eiiiciently and eectively aids the hearing of deafened persons for whombone conduction is indicated. However, this substantially universal result depends upon the response of the vibratory member to the voice currents picked up by the microphone 23.

The stiifness of the diaphragm 21, including the weight of slug 2B and button 29, is so chosen that the diaphragm hv21 not only frees itself from the pole shoe I9 when the excessive freezing pressure is released, but also that the changing flux varies the compliance of the diaphragm to provide the receiver when emplaced on thehead with the general response characteristic of the configuration of the curves shown by Fig. 5, in which the abscissae represent the relative vibrator button and skin surface'vibration while the ordinates represent the frequencies of vibration in cycles per second.

Curve A represents the response of the receiver for a constant voltage input across terminals 2| of the receiver 0 of 0.1 volt. It will be observed from curve A that the receiver has an overall response throughout the intelligible audio-frequency range of about 200 to over 3,000 cycles and has a characteristic which rises to a resonance peak at about 800 cycles per second and then drops oi gradually for the remainder of the audio-frequency range.

In this respect, the receiver of this invention has its resonance peak at about the same frequency as the current bone receivers at the aforementioned input of 0.1 volt, at which the latter function most eiiiciently. In fact, the highest degree of eiiiciency of current bone receivers is coniined to and remains fixed for all inputs in the region just below 1,000 vibrations per second. This has resulted in favored transmission for the vowel sounds, which are strong and hence need not be emphasized, and the unfavored transmission of the consonant sounds, which are weak and need emphasis, since they convey approximately 90% of the message. The overall result is that the message-carrying ability of current bone receivers is poor, although the speech may sound firm and fairly natural.

Although having a peak frequency at 0.1 volt input at approximately the same point, the new receiver of this invention otherwise differs materially in its response to speech, having the remarkable property of accommodating its response to the sounds it transmits in such a way that the weaker message-carrying consonants are emphasized to greatly augment intellgibility over that of current bone receivers without impairing fidelity of reproduction.

This is effected in the new receiver by an automatic shift of the resonance peak toward the higher frequencies above 1,000 cycles for the weaker or consonant sounds from a frequency below 1,000 cycles for a strong vowel sound. In other words, the peak frequency of the curves for different signal levels of the new receiver varies inversely as the signal level within limits, thus having a peak above 1,000 cycles for a low voltage input and a peak below 1,000 cycles for a high voltage input. For example, the long o as in oasis" has a high phonetic energy level and will be reproduced by the receiver according to a high signal level operating curve indicated as A in Fig. 5. The long 'a in oasis" which has a phonetic energy level somewhat below that of the long '5 will be reproduced according to the operating curve corresponding to a lower signal level as indicated by curve As. However. for the weak consonant s, the peak shifts to the right to cross and exceed 1,000 cycles, as shown by the curves below curve A. Thus, in the transmission of the sample word oasis," the relatively strong o has a resonance peak at about 800 C. P. S. as representedby curve A. As' gives way to the less strong sound a, the peak shifts to the right to about 00 C. P. S. asrepresented by the curve Aa. As a. is followed by the weak sibilant is, the peak shifts to the right to about 1200 cycles. as indicated by curve As. The following L although a vowel, is relatively weak, so that the peak shifts somewhat to the left to about 1,100 C. P. S. (curve A1), to return to the right (curve As) as the final s follows. In this way, the messagecarrying consonants are emphasized by the new receiver, and the users hearing is materially aided by the property of dynamic intelligibility that is illustrated by the family of nested curves A.

As. A1 and A, in Fig. 5. The dotted straight line B connecting their peaks also demonstrates the dynamic shift of the peaks from below to above 1,0000. P. S. during speech reception.

The current bone receivers do not have this property of dynamic intelligibility for under the same conditions, with the bone receivers cemented to the skin overlying the mastoid, the resonance peak remains at the same frequency of about 800 cycles per second regardless of the inherent variations in the decibel or voltage input which occurs in speech transmission. In these comparative articulation tests. it was also found that the response curves of the new receiver are broader and flatter than those obtained with bone receivers, thus affording high intelligibility over a much greater range of soft to loud speech.

As stated, the new receiver may be cemented to the head by the adhesive wafer S0 which is circular and is slightly smaller than the button surface, as shown in Figs. 2 and 3. The wafer 30 is coated on both surfaces with a normally tacky pressure-sensitive material| such as a suitable rubber-resin adhesive. One tacky surface oi the wafer 30 is adhered to the outer surface of button 29, which may be slightly concave as shown, and the exposed tacky surface of the Wafer 30 is adapted to be placed against the skin and is suiliciently tacky to hold the unit I0 securely in place as shown in Fig. l, without other support for an indefinite period of time.

Inasmuch as the wafer 30 is tacky on both surfaces and is expendable, it is supplied in the form of cartridges 3l, one of which is illustrated in partial section in Fig. 4. The cartridge 3| consists of four circular sheets of paper, 32 and 33, two of which are folded in half with one half of each abutting the other so that their free halves form a disc which is adhered to one surface of wafer 30 asshown in Fig. 4. The other pair of paper discs 32 and 33 are arranged in the same way and adhered to the opposite surface of the wafer 30. When the wafer 30 is to be applied to the button 29. the paper discs on one side, say 32 and 33, are stripped from the wafer 30, and the resulting exposed tacky surface centered and pressed on the button 29, after which the other paper discs 32 and 33 are stripped oi of the wafer 30, thereby leaving the tacky surface exposed for application to the skin of the user.

Although adhesive mounting is preferred, the pressureless connection between the button 29 and the Vhead may be obtained by mounting the unit on the end of the bow of a spectacle frame, either by cementing it to the outer surface of the bow or by other means.

In operation, the new audiphone receiver of this invention when applied to the head of the user by adhesive wafer 30 or held without pressure in communication therewith, as on the bow of a spectacle frame, otherwise hangs freely since it is supported only by the vibratory contacter l2 so that the remainder of the instrument does not touch the skin. When the voice coil 20 is energized by varying currents generated by the microphone 23. the diaphragm 21 is vibrated and with-it, the button 29.

Under the conditions previously described, the vibrations are transmitted through the skin and underlying bone to the inner ear of the user with a high degree of intelligibility and fidelity, notwithstanding that no headband or other pressure means is employed,

Because the button 29 is attached to the center of the diaphragm 21 by the slug 28. the former partakes of the maximum vibration of the diaphragm and acts as a free-edged piston, imparting to the skin the full amplitude of vibration over its entire area. The diaphragm vibration is maximum at its center portion within the perimeter of the slug 28, and zero at its peripheral support on bead 26.

Also, as the diaphragm is free at its edges, the casing I4 may be rotated to any desired angle. thus permitting angle of the cord to be adjusted to suit the wearer, and it may hang down vertically as shown in Fig. 1, or passed over the ear. or otherwise arranged without disturbing the connection between the button and the skin. For the same reason, when the receiver is pulled away from the skin in order to remove it, the diaphragm is often drawn by adhesion of the wafer to the skin from the peripheral bead 26 to the point where the peripheral flange of button 2S engages clamp ring I5 without distorting the diaphragm which immediately is restored to its seat 26 when released. For the same reason, any tilt of the button 29 relatively to the diaphragm 2l does not permanently distort the diaphragm 2l.

The freedom of vibration of the vibratory member i2 results in little vibration of the magnetic assembly, including its housing i3, so that acoustic feed-back to the microphone from the unit is substantially eliminated.

Although a preferred embodiment of the invention has been illustrated and described herein, it is susceptible of changes in form and detail within the scope of the appended claims.

I claim:

l. In an audiphone receiver. the combination of a contractor adapted to be operatively connected to the skin of the user, a diaphragm carried thereby, magnetic means cooperating with said diaphragm to vibrate the same and support itself on said diaphragm, spacing means between said diaphragm and said magnetic means to provide a ux gap, and electrical means connected to said magnetic means for varying the flux across said gap to vibrate the diaphragm and contactor at audible frequencies, said diaphragm having a compliance varying with the flux to provide a contactor vibration having a response characteristic which has a resonance peak at frequencies below 1,000 cycles per second with constant relatively high voltage input to said electrical means and which has a resonance peak at a higher frequency with constant relatively lower voltage input to said electrical means.

2. In an audiphone receiver, the combination of a contactar adapted to be operatively con nected to the skin f the user, a resilient diaphragm secured thereto. magnetic means ccoperating with said diaphragm to vibrate the same and support itself on said diaphragm. spacing means between said diaphragm and said magnetic means to provide a flux gap, and electrical means connected tc said magnetic means for varying the flux across said gap to vibrate the diaphragm and contacter at audible frequencies, the mass of said contactar and the resiliency of said diaphragm modifying the vibration thereof to provide a response characteristic whose resonance peak shifts from a region below 1,000 cycles per second with a constant relatively high input voltage to said electrical means to a region above 1,000 cycles per second with a relatively4 lower constant input voltage, and vice versa.

3. In an audiphonereceiver, the combination of a vibratory contactar, electrical means adapted -to be energized by varying currents within the audible frequency range and including a. pole face, a `free edge diaphragm connected to said contactar and spaced from said pole face by a narrow gap for vibration by said electrical means, spacing means on said electrical means engaging one surface of said diaphragm for holding the said surface spaced from said pole face against the magnetic traction, and adhesive means interposed between the contacter and skin for holding said contacter in engagement with the skin, whereby the contactor and diaphragm and the magnetic traction constitute the sole support by holding said electrical means onthe skin.

4. In an audiphone receiver, the combination of a vibratory contactor, electrical means adapted to be energized by varying currents within the audible frequency range and having a pole face, a circular diaphragm of exible material connected to said contactor and extending annularly beyond the periphery of the said contacter connection therewith, whereby the flexibility of the diaphragm is confined to the said annularly ex- Itending portion thereof, a circular abutment on said means for supporting said diaphragm adjacent its periphery, and mounting means on said contactor securing the same directly to the skin of the user, whereby the contactor and diaphragm support said means on said abutment.

5. In an audiphone receiver, the combination of a vibratory contactor, electrical means adapted to be energized by varying currents within the audible frequency range and including a pole face, an armature connected to said contacter and spaced from said pole face by a narrow gap for vibration by said electrical means, a diaphragm connected to said armature, an abutment on said electrical means engaging one surface of said diaphragm, and means interposed between the skin of the user and said con-tactor for holding the latter in engagement with the skin, whereby the contactor, armature and diaphragm support said electrical means on said abutment.

6. In an audiphone receiver, the combination of a vibratory contactor. magnetic means having a pole face, an abutment on said magnetic means, a diaphragm normally resting on said abutment in spaced relation to said pole face to. provide a fiux gap therewith and having sufficient spring stillness to free itself from the pole face when freezing pressure is released therefrom, electrical means connected to said magnetic means varying the iiux across said gap to vibrate said diaphragm and contactor at audible frequencies, said contactor vibration having a response characteristic which has a resonance peak at frequencies below 1,000 cycles per second with constant relatively high voltage input to said electrical means and which has a resonance peak at a higher frequency with` constant relatively` lower voltage input to saidelectrical means, and means on said contactor securing the same directly to the skin f the user.

JARVIS M. HAZARD.

REFERENCES CITED The'following references are of record in the file of this patent:

` UNITED STATES PATENTS Number Name Date 2,402,392 Goldschmidt June 18, 1946 2,463,786`v Lybarger Mar. 8, 1949 2,493,734 Pearson Jan. 3, 1950 

